[mufan]

I have a polyurethane that is dispersed in water and I want to replace the water with ethanol.  Since h20 and ethanol are miscible I can't separate them with sep funnel.  I also can't evaporate the water because the polyurethane will cure at this point and it is irreversible.  So does anybody know of a distillation method or some other method that will allow me to substitute ethanol for water in this case?

[taxol7]

I am not a polymer chemist so you will have to forgive me if I am talking rubbish here but have you thought about freeze drying ? Its a process where you cool the solution with dry ice acetone mix and freeze it, then apply high vacuum and sublime the water off to leave the urethane which can then be dissolved in ethanol. Again I am not sure about the conditions required for curing to occur. But there is going to be a stage where the urethane will have to survive without solvent if you want to replace water with ethanol. Good Luck

[alphahydroxy]

I'm no polymer chemist either, but what about vacuum distillation ?

[Bronwen Dekker]

Do polyurethanes "settle" if you centrifuge them?

Do they settle if you apply a vacuum to some sort of filtration apparatus with a sintered glass funnel?

If they do either of these, I suppose you could control the chosen step such that the polyurethane never goes to dryness?

[Yggdrasil]

Could you use dialysis to change solvent?

[Custos]

Would this work? Since it's a dispersion you could decant off most of the water and then add ethanol -- mix and repeat several times until you have diluted out the water to zero.

[tomas]

first, i am not sure i have been understand what you have said!
i think the method that distillation under vacuum you have done.
but i suggest that you'd better make sure what point your product will be bad. and then you can do it better.

[HP]

Cant you use simple filtration of your polymer dispersion and after that to redisperse the concentrated polymer with EtOH...Also what is the dimension of the polymer dispersion - colloidal or macro dispersed particles ?

[mufan]

I've tried filtering but a fine frit won't catch it.  The problem is that the the dispersion consist of micelles.  A surfactant is present in the solution which keeps the polyurethanes from curing as long as water is present.  you can evauate a good bit of the water but at a certain point the water concentration will become too low and the polyurethane will cure.  So I'm trying to replace the water with ethanol as the water leaves.  Tricky i know, maybe not possible.